U.S. patent number 8,875,749 [Application Number 13/225,306] was granted by the patent office on 2014-11-04 for method for the preparation of samples.
This patent grant is currently assigned to Mettler-Toledo AG. The grantee listed for this patent is Siegfried Gluvakov, Bruno Nufer. Invention is credited to Siegfried Gluvakov, Bruno Nufer.
United States Patent |
8,875,749 |
Nufer , et al. |
November 4, 2014 |
Method for the preparation of samples
Abstract
A method for the preparation of samples by means of a
dosage-dispensing device, a weighing system with a load receiver, a
processor unit, a memory unit, and an exchangeable
dosage-dispensing unit. A target container is set on the load
receiver. The dosage-dispensing unit and/or the target container
includes electrically insulating material. The dosage-dispensing
unit has the capability to change positions relative to the load
receiver. While the dosage-dispensing unit is in a first position
and a target container is on the load receiver, a starting weight
value is determined, the dosage-dispensing unit is brought into a
second position, a dosage-dispensing cycle delivers a dosage
material in a predefined amount from the dosage-dispensing unit
into the target container by means of the processor unit, the
dosage-dispensing unit is brought into the first position, and
while the dosage-dispensing unit is at rest in the first position,
an ending weight value is determined.
Inventors: |
Nufer; Bruno (Illnau,
CH), Gluvakov; Siegfried (Neuhaus, CH) |
Applicant: |
Name |
City |
State |
Country |
Type |
Nufer; Bruno
Gluvakov; Siegfried |
Illnau
Neuhaus |
N/A
N/A |
CH
CH |
|
|
Assignee: |
Mettler-Toledo AG (Greifensee,
CH)
|
Family
ID: |
43480864 |
Appl.
No.: |
13/225,306 |
Filed: |
September 2, 2011 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20120055579 A1 |
Mar 8, 2012 |
|
Foreign Application Priority Data
|
|
|
|
|
Sep 2, 2010 [EP] |
|
|
10174992 |
|
Current U.S.
Class: |
141/1; 702/173;
222/181.1; 222/1; 141/94; 141/83; 177/1; 222/77 |
Current CPC
Class: |
G01G
23/00 (20130101); B65B 1/32 (20130101); B65B
3/28 (20130101); G01G 13/003 (20130101); G01G
13/24 (20130101) |
Current International
Class: |
B65B
3/04 (20060101) |
Field of
Search: |
;141/1,2,11,83,94
;222/181.1,1,77,55,59,63,64 ;702/173 ;177/1,25.13 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Maust; Timothy L
Assistant Examiner: Kelly; Timothy P
Attorney, Agent or Firm: Standley Law Group LLP
Claims
What is claimed is:
1. A method for the preparation of samples by means of a
dosage-dispensing device comprising a weighing system with a load
receiver, a processor unit, a memory unit, an ionizer, and an
exchangeable dosage-dispensing unit, wherein one of a target
container set on the load receiver or the dosage-dispensing unit
comprises electrically insulating material, and wherein the
dosage-dispensing unit has the capability to slide or swivel
between a first position and a second position relative to the load
receiver, the method comprising the steps of: (a) receiving at the
processor unit from the weighing system and storing in the memory
unit a starting weight value while the dosage-dispensing unit is at
rest in the first position and the target container is on the load
receiver; (b) after the dosage-dispensing unit is moved to the
second position, transmitting from the processor unit to the
dosage-dispensing unit a request to dispense into the target
container a predetermined amount of mass; (c) after the
dosage-dispensing unit is returned to the first position and is at
rest, receiving at the processor unit from the weighing system an
ending value; and (d) receiving at the processor unit from the
weighing system intermediate weight values when the ionizer is
switched off.
2. The method according to claim 1, further comprising detecting
electrostatic charges by: receiving at the processor unit from the
weighing system a test weight value determined in the second
position and prior to the step of using the processor unit to
deliver a mass from the dosage-dispensing unit; and comparing at
the processor unit the test weight value to the starting weight
value.
3. The method according to claim 1, further comprising subtracting
at the processor unit the starting weight value from the ending
weight value and storing the result in the memory unit or
transmitting the result to an output unit as the weighed mass of
the dosage material.
4. The method according to claim 3, further comprising: calculating
at the processor unit a mass amount of a further dosage material
based on the weighed mass of the dosage material and a desired mix
ratio; replacing the dosage-dispensing unit with the dosage
material that has already been dispensed by a further
dosage-dispensing unit with the further dosage material; and
repeating steps (a)-(d) with the further dosage-dispensing
unit.
5. The method according to claim 3, further comprising: receiving
at the processor unit from the weighing system an error weight
value after the dosage-dispensing process has been completed and
the dosage-dispensing unit is still in the second position;
calculating at the processor unit a correction value based on the
ending weight value, the error weight value and the distance
between the first position and the second position; and calculating
at the processor unit a corrected mass of the dosage material based
on the weighed mass of the dosage material and the correction
value.
6. The method according to claim 5, further comprising calculating
at the processor unit a mass of a solvent to be added based on the
weighed mass or the corrected mass of the dosage material and a
desired concentration.
7. The method according to claim 1, further comprising receiving at
the weighing system a plurality of intermediate weight values and
transmitting the weight values to the processor unit for the
control of the dosage-dispensing process.
8. The method according to claim 7, further comprising: evaluating
at the processor unit at least two intermediate weight values, a
time interval between them, and an aperture cross-section of the
outlet orifice of the dosage-dispensing unit at the times when the
intermediate weight values are measured; and determining at the
processor unit a flow parameter that characterizes the flow
properties of the dosage material.
9. The method according to claim 8, further comprising using the
flow parameter to estimate a time profile for the closure based on
whether the aperture cross-section of the outlet orifice of the
dosage-dispensing unit is closed.
10. The method according to claim 1, further comprising operating
the ionizer during the time when the dosage-dispensing unit is
shifted from the first position into the second position.
11. The method according to claim 10, further comprising switching
the ionizer on and off during the dosage-dispensing process.
12. The method according to claim 11, wherein receiving at the
processor unit a plurality of intermediate weight values comprises
receiving the weight values only while the ionizer is off.
13. A system comprising: a weighing system with a load receiver; a
processor unit in communication with the weighing system; a memory
unit; an ionizer; and an exchangeable dose-dispensing unit
comprising electrically insulating material and with the capability
to slide or swivel between a first position and a second position
relative to the load receiver; the processor unit comprising
executable instructions to: (a) receive at the processor unit from
the weighing system and store in the memory unit a starting weight
value while the dosage-dispensing unit is at rest in the first
position and the target container is on the load receiver; (b)
after the dosage-dispensing unit is moved to the second position,
transmit from the processor unit to the dosage-dispensing unit an
instruction to dispense into the target container a predetermined
amount of mass; (c) after the dosage-dispensing unit is returned to
the first position and is at rest, receive at the processor unit
from the weighing system an ending value; and (d) receive at the
processor unit from the weighing system intermediate weight values
when the ionizer is switched off.
14. The system of claim 13, wherein the dosage-dispensing unit is
arranged above the load receiver of the weighing system and is
movable in relation to the load receiver between a first position
and a second position.
15. The system of claim 14, wherein the dosage-dispensing unit is
constrained in its mobility by a vertical linear guide and is
movable between the first position and the second position by means
of a drive unit.
16. The system of claim 13, wherein the dosage-dispensing unit
comprises a dosage-dispensing head for liquids through which a
quantity of solvent that has been calculated by the processor unit
can be dispensed into the target container.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of a right of priority under 35
USC .sctn.119 from European Patent Application No. 10174992.7,
filed Sep. 2, 2010, the contents of which are incorporated by
reference as if fully recited herein.
TECHNICAL FIELD
The invention concerns a method for the preparation of samples by
means of a dosage-dispensing device, a computer program in which
the method steps are implemented, and a dosage-dispensing device in
which the computer program is stored.
BACKGROUND
Dosage-dispensing devices and dosage-dispensing methods of the
aforementioned kind are commonly known in many fields of industry
and have been in use for years. They include in most cases a
gravimetric measuring instrument, specifically a weighing system,
by means of which the dispensed mass of dosage material is
measured. The amounts of mass to be measured range from tons down
to the smallest quantities of a few micrograms. Especially the
dispensing of minuscule amounts, for example in the development of
new active ingredients, requires the highest precision, as even the
smallest deviation of the mass of the active ingredient can
strongly affect the experiments that are performed after the
dosage-dispensing process. For instance, when substances are mixed
together, the reaction rates can vary considerably as a result of
mass deviations; or in clinical tests, the effects on the organism
of the test person can deviate considerably from the expected
outcome, to name only a few examples.
In order to perform the experiments, one has to prepare a large
number of samples. For example, small amounts of pulverous
substances are dispensed into a target container, where they are
dissolved by adding a solvent. The sample which has been prepared
in this manner is subsequently analyzed, for example in an HPLC
(High Performance Liquid Chromatography) analyzer.
A dosage-dispensing device capable of measuring out minute amounts
of mass and a method of optimizing a dosage-dispensing process are
disclosed in EP 1 947 427 A1. The dosage-dispensing device includes
a weighing system with a load receiver, a processor unit, a memory
unit, and an exchangeable dosage-dispensing unit. The
dosage-dispensing unit is arranged above the load receiver on which
a target container can be set in place. So that target containers
of different heights can be used, the dosage-dispensing unit is
height-adjustable in relation to the load receiver.
Extraneous influences play an important part when extremely small
masses are measured out. Air movements, temperature fluctuations
and the like can strongly influence the weighing result or, more
specifically, the weight values determined by the weighing system.
If these weight values are used for the control of the
dosage-dispensing process and as a basis for the amount or mass of
solvent that is to be subsequently added, the aforementioned
extraneous factors can lead to faulty samples.
When measuring out pulverous substances with the dosage-dispensing
device of the foregoing description, it was found that
electrostatic effects, too, can introduce significant errors into
the weighing results. If the target container and/or the
dosage-dispensing unit include materials that are not electrically
conductive, they can become electrostatically charged. This can
have the consequence that the target container and the
dosage-dispensing unit mutually repel or attract each other.
Accordingly, the weighing system will measure values that are
higher or lower than the mass that is actually present in the
target container.
As a solution to this problem, ionizers are being offered by means
of which the ambient air of the dosage-dispensing unit and the
target container is ionized, whereby the static charges can be
effectively eliminated. However, as these ionizers use high voltage
levels and therefore generate an electromagnetic field, their
operation can likewise have a harmful influence on the weight
values of the weighing system. Furthermore, the ion flow of the
ionizer can set air masses into motion and the latter can exert a
force on the load receiver.
In a further approach to solve this problem, all components of the
dosage-dispensing device, the dosage-dispensing unit and the target
container are made electrically conductive and are connected to
ground. This usually leads to very good results. However, it
involves the application of metallic coatings or the fabrication of
metal parts, which increases the cost considerably, since
non-conductive materials have to be coated with a layer of
conductive material, or the respective parts have to be made of
metal.
In addition, extensive experiments have shown that the ability to
accumulate electrostatic charges is not limited to the
dosage-dispensing unit and/or the target container. There are also
some pulverous substances which are critical in regard to their
electrostatic behavior and can build up a significant electrostatic
charge as a result of break-up and friction effects during the
dispensing process. Even with the use of electrically conductive,
grounded target containers or dosage-dispensing units and/or an
ionizer, no satisfactory solution has been found for this problem.
For example, when measuring out paracetamol (also known as
acetaminophen) in dosage quantities of 12 mg, deviations due to
electrostatic effects could be observed which amounted to as much
as 40% of the specified mass.
SUMMARY OF THE INVENTION
The present invention therefore has the objective of proposing a
method which serves to prepare samples by means of a
dosage-dispensing device and allows an extremely precise
measurement of the amount of dosage material dispensed into the
target container. A further objective is to create a
dosage-dispensing device with the capability to carry out the
method. This task is solved with a method, a computer program, and
a dosage-dispensing device that have the features described in the
independent patent claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Different embodiments of the dosage dispensing device and method
are described in more detail by referring to the attached drawings,
wherein:
FIG. 1 represents a dosage-dispensing device according to the
invention with a drive device and with two source containers of
different lengths that are equipped with dosage-dispensing heads,
with the dispensing heads being shown separate from the drive
device;
FIG. 2 shows a simplified representation of the dosage-dispensing
device of FIG. 1 in side view to illustrate the first position and
the second position, including the drive unit for changing the
position of the dosage-dispensing unit;
FIG. 3 represents a flowchart diagram of the method according to an
example embodiment of the invention; and
FIG. 4 represents a detailed flowchart of the method according to
an example embodiment of the invention including further possible
process steps of the kind that could be implemented in a computer
program.
DETAILED DESCRIPTION
To execute the method for the preparation of samples, a
dosage-dispensing device needs to be available which includes a
weighing system with a load receiver, a processor unit, a memory
unit, and an exchangeable dosage-dispensing unit. A target
container can be set on the load receiver. The dosage-dispensing
unit and/or the target container can include electrically
insulating material. The dosage-dispensing unit is arranged above
the load receiver with the capability to slide or swivel between a
first position and a second position relative to the load
receiver.
Under the method for the preparation of samples:
while the dosage-dispensing unit is at rest in the first position
and a target container is in place on the load receiver, a starting
weight value is determined by the weighing system and stored in the
memory unit;
the dosage-dispensing unit is brought into the second position;
a dosage-dispensing cycle is performed and dosage material is
delivered from the dosage-dispensing unit into the target container
in accordance with a predefined amount of mass by means of the
processor unit;
the dosage-dispensing unit is brought into the first position;
and
while the dosage-dispensing unit is at rest in the first position,
an ending weight value is determined by the weighing system.
The predefined mass is the target value which is set by the user by
making an entry in an input unit of the dosage-dispensing device.
The method is based on the realization that in the analysis of
samples the prepared overall sample mass is not so much of a
factor, but that it is critical to know the exact concentration of
the substance dissolved in the solvent. In order to be able to
calculate the exact concentration, it is therefore necessary that
the respective masses of the substance and of the solvent can be
measured with the highest possible accuracy.
So that no dosage material is spilled during the dosage-dispensing
process, the dosage-dispensing unit--more specifically its delivery
orifice--needs to be located very closely above the fill opening of
the target container. Thus, the second position also depends on the
height of the target container standing on the load receiver. As a
result of sliding or swiveling the dosage-dispensing unit relative
to the load receiver as specified in the invention, a precise
measurement of the actually dispensed mass is made possible,
because the influence of electrostatic attraction forces decreases
quadratically with the increased distance between the
dosage-dispensing unit and the target container. Accordingly, in a
method according to an example embodiment of the invention, the
starting and ending weight values which are used for the
calculation of the mass that is actually present in the target
container are always measured in the first position, where the
dosage-dispensing unit is at its maximum distance from the target
container and from the load receiver.
Subsequently, the processor unit can subtract the starting weight
value from the ending weight value. The result, which represents
the weighed mass of the dosage material, is then stored in the
memory unit or transmitted to an output unit or a process control
system. The weighed mass is an uncorrected actual value for the
amount of dosage material in the target container. This value is
referred to as uncorrected because the weight values measured in
the first position can still include errors due to electrostatic
charges, as the distance between the first and second positions
should be kept within reasonable limits in order to restrict the
dosage-dispensing device to a practical overall size. However, in
most cases the mass is adequately determined as an uncorrected
actual value.
To provide the capability for preparing mixtures of dosage
materials, the method of the foregoing description can be extended
to include further steps, specifically:
based on the weighed mass of the dosage material and a desired mix
ratio, the mass amount of a further dosage material is calculated
by the processor unit;
the dosage-dispensing unit with the dosage material that has
already been dispensed is replaced by a further dosage-dispensing
unit with the further dosage material;
the steps of the sequence described above are repeated with the
further dosage-dispensing unit.
In the present context, the term "mixture" means a mix of at least
two solid, paste-like, or liquid substances. Of course, one of the
substances can be solid while the other is liquid. A substance to
which a solvent has been added is referred to herein as a solution,
regardless of whether or not the substance is dissolved in the
solvent.
The first and second positions can also be used to establish
whether electrostatic charges are even present. This is possible
with a simple test. If the weighing system delivers identical
weight values for the first position and the second position
(provided that no substance is being discharged from the
dosage-dispensing unit), this indicates an absence or only a small
accumulation of electrostatic charges. Accordingly, a test value
which is registered in the second position is compared to the
starting weight value. If the two weight values differ from each
other, the dosage-dispensing process can be blocked and the user
can be warned. Of course, it is also possible that an ionizer which
is arranged in the dosage-dispensing device is switched on either
automatically or by intervention of the user if electrostatic
charges have been detected in the comparison described here.
Even if the weight values for the calculation of the amount of
dosage material dispensed are measured in the first position,
electrostatic forces that may be present can still affect the
weighing system to a minor extent. With the help of Coulomb's law,
the values measured in the first and second positions allow a
determination and quantification of the electrostatic forces that
come to bear in the first position. The method according to an
example embodiment of the invention can be extended with the
further steps, wherein:
after the dosage-dispensing process has been completed, an error
value for the weight is determined in the second position by the
weighing system;
based on the ending weight value, the error value and the distance
between the first and second positions a correction value is
calculated; and
based on the weighed mass of the dosage material and the correction
value, the corrected mass of the dosage material is calculated.
Further, based on the weighed mass or the corrected mass of the
dosage material and a desired concentration, the mass of a solvent
that needs to be added can be calculated by the processor unit.
To control the dosage-dispensing process, the weighing system can
acquire intermediate weight values continuously, at discrete,
event-triggered, or random intervals during the dosage-dispensing
process, and the intermediate weight values can be entered into the
processor unit for the control of the dosage-dispensing process. Of
course, the intermediate weight values, too, can be corrected with
a previously determined correction value.
The intermediate weight values can be used in different ways. The
easiest approach is to directly actuate a shutter body of the
dosage-dispensing unit, so that the shutter body closes off the
outlet opening as soon as the intermediate weight value is equal to
the predefined value. However, this method normally causes an
overshooting of the predefined value. More precise results can be
achieved by estimating ahead when the outlet orifice will have to
be closed. This requires an evaluation of at least two intermediate
weight values, the time interval between them, and the aperture
cross-section of the outlet orifice of the dosage-dispensing unit
at the times when the intermediate weight values were measured.
Based on this information, a flow parameter can be determined which
characterizes the flow properties of the dosage material.
Subsequently, a time profile for the closing can be estimated by
means of the flow parameter. The aperture of the dosage-dispensing
unit is then closed down according to this time profile.
Of course, the dosage-dispensing device can include an ionizer, so
that electrostatic charges can be neutralized as much as possible
already before the start of the dosage-dispensing process. The
ionizer is preferably switched on when the dosage-dispensing unit
is shifted from the first to the second position.
The ionizer can also be switched on and off periodically during the
dosage-dispensing process. However, in view of the aforementioned
side effects, the measurement of the intermediate weight values
preferably takes place only when the ionizer is switched off.
The method according to an example embodiment of the invention and
its individual steps can be implemented in a computer program which
is executable in the processor unit of a dosage-dispensing device
for the preparation of the samples. This allows the user to select
and assemble the desired process steps from the many that are
available, but the following steps are typically included:
while the dosage-dispensing unit is at rest in the first position
and a target container is in place on the load receiver, a starting
weight value is measured by the weighing system and is stored in
the memory unit;
the dosage-dispensing unit is brought into the second position;
a dosage-dispensing process is performed, wherein under the control
of the processor unit dosage-material of a predefined mass is
dispensed from the dosage-dispensing unit into the target
container;
the dosage-dispensing unit is brought into the first position;
and
while the dosage-dispensing unit is at rest in the first position,
an ending weight value is measured by the weighing system.
The computer program can be used in a dosage-dispensing device. The
latter includes at least a weighing system, a processor unit, a
memory unit, and an exchangeable dosage-dispensing unit, wherein
the dosage-dispensing unit is arranged above a load receiver of the
weighing system and is capable of being shifted or swiveled between
a first position and a second position. The computer program is
preferably stored in the memory unit. However, this does not mean
that the program always has to be stored in the memory unit. It can
also be stored on a data carrier or server and be made accessible
to the processor unit through suitable means.
The dosage-dispensing device is preferably equipped with a holder
device to which a dosage-dispensing unit can be interchangeably
connected. The holder device can be configured so that the movement
of the holder device, and thus also of the connected
dosage-dispensing device, is constrained by a vertical linear guide
so as to be movable between the first position and the second
position by means of a drive unit.
To provide a stable hold in the first position and in the second
position, the drive unit preferably includes a self-locking spindle
for the conversion of rotary into linear motion.
For the complete preparation of a sample by means of the
dosage-dispensing device, the latter is capable of dispensing
liquids. The dosage-dispensing device can therefore also include a
dosage-dispensing head for liquids by means of which a quantity of
solvent that has been calculated by the processor unit can be
dispensed into the target container.
Details of the method according to an example embodiment of the
invention and the dosage-dispensing device according to an example
embodiment of the invention are presented through the examples of
embodiments illustrated in the drawings and described
hereinafter.
FIG. 1 shows a dosage-dispensing device 100 which has a drive
device 150 designed for a dosage-dispensing unit 105, 105' to be
installed and also to be removed again. The dosage-dispensing unit
105, 105' includes a dosage-dispensing head 122 and a source
container 110, 110'. Also shown in the drawing is a
liquid-dispensing head 185 which can be supplied with a liquid
through a hose connector 186. The liquid-dispensing head 185 has an
outside contour shape that matches the shape of the
dosage-dispensing unit 105, 105' to the extent that the
liquid-dispensing head 185 can likewise be inserted into the drive
device 150. A magnet valve (not shown in the drawing) is arranged
inside the liquid-dispensing head 185 to control the mass flow
rate.
The drive device 150 has an upper part 157 and a lower part 158. In
the operating position of the dosage-dispensing device 100, the two
parts are capable of linear movement away from each other and
towards each other in an essentially vertical direction. This makes
it possible to use source containers 110, 110' of different
lengths. To allow an easy exchange of the dosage-dispensing unit
105, 105' and a safe and accurate dispensing operation, the
dosage-dispensing unit 105, 105' and the drive device 150 should be
equipped with suitable mechanical--or, if necessary, mechanical as
well as electrical--connector elements designed for form-fitting
engagement with each other. The dosage-dispensing unit 105, 105'
has at least a first form-fitting element 111 which, by means of a
first counterpart 151 that is formed on or connected to the upper
part 157, is held in a defined position in a horizontal plane
(relative to the operating position of the dosage-dispensing device
100). The dosage-dispensing unit 105, 105' further includes at
least a second form-fitting element 121 which is spatially
positioned relative to the drive device 150 by means of a second
counterpart 181 that is formed on or connected to the lower part
158. As a result of this arrangement, the dosage-dispensing unit
105, 105', specifically its outlet orifice for the delivery of
dosage material, is precisely aligned relative to a target
container 200. Arranged at the second counterpart 181 is an ionizer
250, which helps to at least reduce electrostatic charges of the
dosage-dispensing unit and/or the target container. The
dosage-dispensing device 100 is connected to an input/output unit
270 through which data can be entered such as for example a
predefined and the desired mass tolerance as well as mix ratios and
desired concentrations, and which provides an indication when the
dosage-dispensing process or the sample preparation has been
completed. In addition, many different kinds of information can be
called up or entered by way of the input/output unit 270. In
addition, a processor unit 165 of the dosage-dispensing device 100
can generate different messages and warnings and pass them on to
the user by way of the input/output unit 270.
The processor unit 165 also controls and regulates the entire
sample preparation, in particular the dosage-dispensing process. To
perform this function, a computer program that is stored in the
memory unit 166 is called up and the process steps that are
implemented in it are executed. Also, various items of information
that depend on the currently performed process step are called up
through the processor unit 165, for example mass data that are
requested from the user through the input/output unit 270, or
intermediate weight values of the dosage-dispensing process which
come from a weighing system 190.
The source container 110 in FIG. 1 has a basically cylindrical
shape. However, other shapes for the source container are also
possible, for example with a square, hexagonal or octagonal
cross-section on the outside and inside. After the dispensing head
122 with the source container 110, 110' has been seated in the
drive device 150, its longitudinal axis is oriented vertically in
the operating position of the apparatus, the dispensing head 122
being arranged at the second end of the source container 110, 110'.
Incorporated in the dispensing head 122 is a shutter body (not
shown in the drawing) which can be set into rotation by a drive
source. The shutter body is connected to a shutter shaft 132 that
is movably constrained in the source container 110. The body of the
source container 110 is designed with a tubular shape and is closed
off at the top by a lid 113. The lid 113 contains a pass-through
opening 130 in which the end of the shutter shaft 132 that is
farthest from the shutter body is rotatably constrained and
protrudes to the outside of the source container 110. This end of
the shutter shaft 132 carries a coupling part 131 which in this
example is configured as a square profile section. At least during
the dosage-dispensing process, the coupling part 131 is connected
through a coupling socket 154 with the drive source 155 that is
incorporated in the drive device 150. To allow the coupling to be
engaged, the drive source 155 or at least a drive shaft 156
connected to the drive source should be capable of linear vertical
movement (relative to the operating position). Of course, instead
of the square profile section, any of the known form-locking or
friction-based couplers could be used, provided its coupling halves
are easily separable.
To prevent the first form-fitting element 111 from slipping out of
the first counter part 151, a spring-biased retainer latch 153
pushes the form-fitting element 111 against a slot bottom 152 when
the dosage-dispensing unit 105, 105' is seated in place. To remove
the dosage-dispensing unit 105, 105' from the drive device 150, the
retaining latch 153 can be opened electromechanically or
pneumatically. As shown in FIG. 1, with a suitable design of the
retainer nose, the retainer latch 153 can be pushed aside by the
form-fitting element 111 by applying a considerable amount of force
for the removal of the dosage-dispensing unit 105, 105'. The
spring-biased retainer latch 153 and/or the slot bottom 152 can in
addition be equipped with electrical contacts which--when the
dosage-dispensing unit 105, 105' is seated in place--join up with
matching contacts that are arranged at the first form-fitting
element 111 or at the source container 110, whereby an electrical
connection is established between the dosage-dispensing unit 105,
105' and the drive device 150. An electrical connection of this
kind can be used to connect the dosage-dispensing unit 105, 105' to
ground or, as will be described below, also to connect to a memory
module 115, 115', 123 that is arranged in or at the
dosage-dispensing unit 105, 105'. In addition to storing a flow
parameter, this memory module 115, 115', 123 can also be used to
store the length of the source container 110, 110', so that the
drive device 150 can automatically adapt itself to the different
lengths of the source containers 110, 110'. The same applies of
course also to the liquid-dispensing head 185.
The drive device 150 further includes a locking device 160 which,
when the dosage-dispensing unit 105, 105' is seated in place, bears
against the lid 113 and secures the dosage-dispensing unit 105,
105' against dislocation in the vertical direction. As already
mentioned in regard to the retainer latch 153, the locking device
160 can likewise be equipped with additional electrical contacts
and connections to the memory module 115, 115', 123 and can be
actuated electromechanically or pneumatically.
Furthermore, there is a notch 114 formed on the lid 113. When the
dosage-dispensing unit 105, 105' is seated in place, this notch 114
is engaged by a rotation lock 170 which serves to take up and
counteract the torque that is exerted on the dosage-dispensing unit
105, 105' by the drive source 155. The rotation lock 170 is
configured in this example as a simple spring latch, so that in the
process of setting the dosage-dispensing unit 105, 105' in place,
the position of the notch 114 relative to the rotation lock 170 is
of no concern. As soon as the drive source 155 is coupled to the
shutter shaft 132 by way of a drive shaft 156 and a torque is
acting on the shutter shaft 132, the dosage-dispensing unit 105,
105' is taken along until the rotation lock 170 snaps into
engagement. Of course, the dosage-dispensing unit 105, 105' can
also be turned manually into the correct position. Besides a spring
latch, one could also use bolts, pins, gripping claws and the like
for the rotation lock 170. In addition, the rotation lock 170 could
also have an electrical connection to the memory module 115, 115',
123, analogous to the connection of the retainer latch 153
described above. As an additional function, the rotation lock 170
shown here acts at the same time as an overload release for the
drive source in case the shutter shaft 132 gets blocked in the
dosage-dispensing unit 105, 105'. Of course, the notch 114 can be
formed at any desired location of the dosage-dispensing unit 105,
105', and the rotation lock 170 can be arranged at an appropriately
matched position on the drive device 150.
However, the memory module 115, 115', 123 does not necessarily have
to be physically connected to the processor unit 165 of the
dosage-dispensing device 100 through an electrical conductor such
as a signal cable or a bus system and the like. It is also possible
to use a wireless connection, for example by way of a read/write
device 175 operating inductively or through radio transmission. In
particular, a device based on RFID transponder technology suggests
itself for this purpose.
To collect the respective input variables for the regulation and
control of the dosage-dispensing process, the drive device 150 has
an electrical connection (not shown in the drawing) to the weighing
system 190 on whose load receiver 191 the target container 200 is
placed. The target container 200 can include a target container
memory module 201 which is preferably accessed through a wireless
connection, for example also through the read/write device 175, and
in which characterizing attributes of the prepared sample can be
stored, such as the designation of the substance, the mix ratio,
the solvent, the concentration of the solution, the expiration date
or a flow parameter of the substance.
A linear-guiding device 159 is arranged between the drive device
150 and the weighing system 190 and mechanically connects the two
units. The linear-guiding device 159 makes it possible to use
target containers 200 of different shapes and with different
container heights. The arrangement further allows the
dosage-dispensing unit 105, 105' or the liquid-dispensing head 185
to be raised to a sufficient distance from the target container
200, so that weight values can be determined by the weighing system
190 with minimal or no errors due to the forces of
electrostatically charged parts. Of course, it is also possible to
choose an arrangement that deviates from FIG. 1, where the weighing
system 190 is mechanically separate from the drive device 150. This
avoids the problem of vibrations of the drive device 150 being
transmitted to the weighing system 190 during the dispensing
process, whereby the weight values and/or the response time of the
weighing system 190 could be negatively affected. The position of
the dosage-dispensing unit 105, 105' where its distance from the
target container 200 and from the load receiver 191 is sufficient
for the determination of the weight values is defined as the first
position. The position during the dispensing process, where the
dosage-dispensing unit 105, 105' is as close as possible to the
target container 200 and the load receiver 191, is defined as the
second position. A drive unit with a threaded spindle 188 serves to
move the dosage-dispensing unit from the first to the second
position. Of course, instead of the threaded spindle 188 and the
linear-guiding device 159, there can be a swivel hinge (not shown
in the drawing) arranged between the drive device 150 and the
weighing system 190, so that the drive device 150 can be swiveled
between different positions relative to the weighing system 190.
With the swivel arrangement, the drive device 150 and the
dosage-dispensing unit 105, 105' that is seated in it can be
swiveled into a first and a second position as indicated by the
dash-dotted double arrow X. Of course, a horizontal linear sliding
arrangement of the dosage-dispensing unit 105, 105' relative to the
weighing system 190 is also a possible alternative.
The first position OP and the second position UP are illustrated in
FIG. 2 which shows the dosage-dispensing device 100 in a
schematically simplified side view. Those parts that are identical
to the parts shown in FIG. 1 carry the same reference symbols again
in FIG. 2. The second position UP nearly equals the container
height of the target container 200, as the outlet orifice 124 of
the dosage-dispensing unit 105 should during the dispensing process
be positioned at the smallest possible distance r.sub.2 next to the
fill opening of the target container 200, but without touching the
latter. The first position OP preferably represents the maximally
possible distance r.sub.1 of the fill opening 124 from the target
container 200, or the maximum distance from the load receiver 191
that is achievable with the given length of the linear-guiding
device. However, as described below in reference to FIG. 4, it is
also possible to define another, smaller distance as the first
position OP, if the influence of electrostatic forces is small or
if it can be accounted for by means of a correction value. Of
course, the method according to an example embodiment of the
invention can also be performed with an arrangement where the
dosage-dispensing unit 105, 105' can be swiveled laterally relative
to the target container 200, in which case the dosage-dispensing
unit 105, 105' in the second position is located exactly above the
target container 200. Accordingly the first position OP is
represented by the swiveled position in which the dosage-dispensing
unit 105, 105' is laterally offset from the target container
200.
Arranged in the housing 193 of the weighing system 190 (shown in a
sectional view) is a weighing cell 192 which is mechanically
connected to the load receiver 191, converting the load resting on
the load receiver 191 into a weighing signal. The weighing signal
is passed on to the processor unit 165 where it is processed
further, for example into weight values. Also arranged in the
housing 193 is a drive unit 187 with the threaded spindle 188. The
latter passes through the housing 193 and is engaged by a spindle
nut 189 which is arranged in the lower part 158 of the drive device
150.
FIG. 3 represents a flowchart diagram of the method 300 according
to an example embodiment of the invention, containing only those
steps that are absolutely necessary. Beginning at the start 310,
the user is asked in a first step 311 to enter the predefined mass
of dosage material. In a second step 312, the user needs to set a
new dosage-dispensing unit into the drive device. The third step
313 consists of a check to determine whether the dosage-dispensing
unit is located in the first position. If this is not the case,
then the dosage-dispensing unit--more specifically the holder
device in which the dosage-dispensing unit is seated--needs to be
moved into the first position. In a fourth step 314, a target
container is set on the load receiver and a starting weight value
is established. Next, in the fifth step 315, the dosage-dispensing
unit is moved into the second position with the help of the drive
unit. A test is now made in step 340, in which a test weight value
is determined and compared. If the starting weight value and the
test weight value are found to be identical (provided that no
substance has been discharged yet from the dosage-dispensing unit),
this indicates an absence or only a small accumulation of
electrostatic charges. If the two weight values are different from
each other, the dispensing process can be blocked and the user can
be warned. Obviously, it is also possible that an ionizer which is
arranged in the dosage-dispensing device is switched on, either
automatically or by intervention of the user, if electrostatic
charges have been detected in the comparison described here.
In the sixth step 316, the dosage-dispensing program is started and
the dosage material is delivered into the target container in
accordance with the predefined mass that was entered in the first
step 311. After the dispensing process has been completed, the
dosage-dispensing unit is returned to the first position in step
317. Next, the weighing system measures an ending weight value in
an eighth step 318. To calculate the weighed mass of dosage
material, the starting weight value is subtracted from the ending
weight value in a ninth step 319, which is performed by the
processor unit. This calculated value which represents the weighed
mass of dosage material can be transmitted directly to a further
processing stage, for example to the indicator unit, or it can be
stored in the memory unit for later processing. After the
calculation of the weighed mass of dosage material the flowchart of
the absolutely essential steps ends at 320.
Due to the influence of electrostatic charges, the weighed mass can
deviate from the predefined mass. In order to bring the weighed
mass of dosage material into closer agreement with the predefined
mass, the steps 312 to 319 of the foregoing description can be
repeated until the value of the weighed mass matches the predefined
mass within a given tolerance range. This loop is indicated by a
broken line.
FIG. 4 illustrates how the flowchart of FIG. 3 can be expanded with
additional process steps. FIG. 4 shows a detailed flowchart of the
method 400 according to an example embodiment of the invention with
further possible steps of the kind that can be implemented in a
computer program. The steps that have already been discussed in the
context of FIG. 3 are identified by the same reference symbols and
are not explained again.
The four mixture-preparation steps 411, 412, 413 and 414 represent
a first addition to the steps of flowchart 300. In the first
mixture-preparation step 411, which occurs after the ninth step 319
or after the third correction step 423 which will be explained
below, the user, the memory unit, or a higher-level process control
system is interrogated and a yes/no response is requested whether a
mixture is to be prepared with the substance already dispensed into
the target container. If the answer is affirmative, the subsequent
mixture-preparation steps 412, 413, 414 are executed and the second
through ninth steps 312 to 319 are repeated.
In the second mixture-preparation step 412, the program calls for
the mix ratio as an input from the user, the memory unit, or from a
higher-level process control system. In the third
mixture-preparation step 413, the dosage-dispensing unit that is
currently seated in the holder device is removed. In the fourth
mixture-preparation step 414, the mass amount of the next dosage
material to be added is calculated based on the weighed mass of
dosage material and the mix ratio. This is followed by the second
through ninth steps 312 to 319.
After the second pass through the ninth step 319 has been
completed, the interrogation of the second mixture-preparation step
412 takes place for the second time, so that a further substance
can be added to the mixture of two substances in the target
container. Analogous to the loop described in FIG. 3, it is also
possible to use several passes with the same dosage-dispensing unit
in order to obtain the desired mix ratio within a predefined
mix-ratio tolerance.
Even if the starting weight value and the ending weight value are
determined in the first position, they can still include an error,
as the distance between the first position and the second position
is subject to design limitations. This residual error can be
corrected by means of the correction steps 421, 422 and 423, so
that the weighed mass in its non-corrected actual amount can still
be rectified. The first correction step 421, which occurs between
the sixth step 316 and the seventh step 317, serves to establish an
error weight value immediately after the dosage-dispensing process
when the dosage-dispensing unit is still in the second position.
The error weight value and the ending weight value determined in
the eighth step 318 are now processed in the second correction step
422.
Based on Coulomb's law, which is mathematically expressed as
.times..pi..times..times..times..times. ##EQU00001##
the electrostatic force which acts in the upper position, or the
correction value, can be calculated based on the distance r.sub.1
of the first position from the load receiver, the distance r.sub.2
of the second position from the load receiver, and the difference
of the measured weighing error and the ending weight value. Based
on Coulomb's law, one arrives at the following approximate
correction value, which is expressed in the same units as the
weight values and can be subtracted from the weighed mass
determined in the ninth step 319:
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times. ##EQU00002##
The subtraction occurs in the third correction step 423 and leads
to the value of the corrected mass which is transmitted to an
indicator unit and/or stored in the memory unit and/or passed on to
the process control system.
After all of the substance doses have been delivered, a measured
quantity of solvent may in some cases have to be added to the
target container in order to complete the preparation of the
sample. Depending on whether or not the correction steps 421, 422
and 423 were applied, the mass of the selected solvent can be
calculated based on the weighed mass or the corrected mass and the
desired concentration. The program calls for the concentration and
the selected solvent in the first sample-preparation step 431. The
calculation of the mass of the solvent and the dispensing of the
solvent occurs in the second sample-preparation step 432, after
which the process has reached its end 320.
It should further be mentioned that the ionizer shown in FIG. 1 can
be used during the different steps or between all of the steps of
the method 400. The use of the ionizer, indicated as step 441, can
occur for example during the third step 313, the fifth step 315 and
the sixth step 316.
Obviously, the place of the user can also be taken by a handling
system and a process control system for a fully automated sample
preparation.
LIST OF REFERENCE SYMBOLS
100 dosage-dispensing device 105,105' dosage-dispensing unit
110',110 source container 111 first form-fitting element 113 lid
114 notch 115',115 memory module 121 second form-fitting element
122 dispensing head 123 memory module 124 outlet orifice 130
pass-through opening 131 coupling part 132 shutter shaft 150 drive
device 151 first counterpart 152 slot bottom 153 retainer latch 154
coupling socket 155 drive source 156 drive shaft 157 upper part 158
lower part 159 linear-guiding device 160 locking device 165
processor unit 166 memory unit 170 rotation lock 175 read-/write
device 181 second counterpart 185 liquid-dispensing head 186 hose
connector 187 drive unit 188 threaded spindle 189 spindle nut 190
weighing system 191 load receiver 192 weighing cell 193 housing 200
target container 201 target container memory unit 250 ionizer 270
input-/output unit 400, 300 method 310 start 311 step 1: enter
predefined mass of dosage material 312 step 2: install new
dosage-dispensing unit 313 step 3: bring dosage-dispensing unit
into first position 314 step 4: set target container in place and
determine starting weight value 315 step 5: bring dosage-dispensing
unit into second position 316 step 6: dosage-dispensing process 317
step 7: bring dosage-dispensing unit into first position 318 step
8: determine ending weight value 319 step 9: calculate the weighed
mass of dosage material 320 end 340 test: acquire test weight value
and compare to starting weight value 411 mixture preparation step
1: interrogation whether or not a powder mixture is desired 412
mixture preparation step 2: entry/input request for mix ratio 413
mixture preparation step 3: remove the currently installed
dosage-dispensing unit 414 mixture preparation step 4: calculate
mass of substance to be added 421 correction step 1: determine
error weight value 422 correction step 2: calculate correction
value 423 correction step 4: calculate corrected mass 431 sample
preparation step 1: request input of desired concentration 432
sample preparation step 2: calculate and dispense required amount
of solvent 441 use of ionizer
* * * * *